The present invention relates to an improved synthetic turf which simulates grass for both indoor and outdoor use as a recreational and sports surface. More particularly, this invention relates to an improved filament for making such synthetic turf which provides increased resistance to cracking and fibrillation.
Simulated-grass carpeting or synthetic turf for recreational uses such as football, baseball, soccer and field hockey is well known. Conventional synthetic turf surfaces generally include a weather-resistant, cushioned backing, or pad, onto which is adhesively joined a fabric backing, or substrate, into which are anchored and from which extend a plurality of relatively heavy denier synthetic polymer filaments simulating grass. These synthetic turfs are produced for the most part by conventional weaving, knitting or tufting operations employing either a single filament, a package of filaments, or a yarn of twisted or braided filaments.
Conventional synthetic turf filaments are uniformly manufactured having substantially rectangular cross sections, such as disclosed in carter. et al., U.S. Pat. No. 3,551,263, and Vinicki, U.S. Pat. Nos. 3,513,061 and 3,513,062. Such filaments are typically manufactured by an extrusion process from polymers such as polyamides, polyesters, and polypropylene. Typically, such filaments may be roughened, ribbed, treated with surfactants, texturized or otherwise finished to facilitate fabrication and prevent footwear slippage. Finally, such filaments may also be striated or scored to reduce glare or sheen.
It has been discovered that over the life of synthetic turf made of filaments having rectangular cross sections, the combination of sunlight and wear results in accelerated xe2x80x9cgreen dustingxe2x80x9d or fibrillation (cross sectional crack propagation) of the filaments. Accelerated fibrillation is especially common in areas of relatively heavy wear such as the areas immediately surrounding the goal on soccer or field hockey pitches or the middle portions of football fields. Accelerated fibrillation significantly decreases the useful life of the turf and makes it appear worn and frayed.
High exposure to ultra violet light (UV) is a prime factor in the acceleration of filament fibrillation. UV penetrates into the exposed surfaces of a filament and, over time, unbinds molecular bonds within the polymer, causing a decrease in the molecular weight of the polymers of the filament at those portions affected by UV. This decrease in molecular weight weakens that portion of the filament, making it more susceptible to the cracking inevitably caused by wear over time. Cracks developing in the filament expose more surface area of the filament to UV which, in turn, accelerates the weakening process. Therefore, in order to increase the useful life of synthetic turf surfaces, it is desirable to increase filament resistance to fibrillation resulting from wear and/or UV exposure.
A common method of avoiding or at least delaying fibrillation is to increase the filament""s resistance to UV through the addition to the polymer of one or more well known UV absorbers, UV stabilizers or heat stabilizers. This technique is common in the industry and may be employed in conjunction with the present invention.
Increased resistance to cracking and fibrillation is also found to be directly related to the thickness of the filament. However, even small increases in the thickness of a rectangular filament quickly makes the filament unsuitably stiff and abrasive for practical use in synthetic turf. As disclosed in Carter, et al., and Vinicki, rectangular cross sectional filaments more than 0.003 inches thick are undesirable.
Similarly, rounded or oval filaments are undesirable because they tend to become too stiff and abrasive in deniers of suitable weight.
The present invention is a synthetic turf having filaments with substantially diamond shaped cross sections which surprisingly provide increased resistance to cracking and fibrillation while retaining useful flexibility and abrasion characteristics.
It is, therefore, an object of the present invention to provide a synthetic turf, with filaments having a substantially diamond shaped cross section.
It is a further object of the present invention to provide a synthetic turf filament which provides improved resistance to cracking and fibrillation.
It is also an object of the present invention to provide a synthetic turf filament which can be employed in conventional weaving, knitting or tufting processes to produce synthetic turf.
These and other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the accompanying description of the preferred embodiment of the present invention is read in conjunction with the accompanying drawings.